ESTRO 2025 - Abstract Book

S3510

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTRO 2025

collimated standard arcs (Arc+Coll) and (3) collimated standard 3-beam plans. For the H&N case, we additionally created a collimated 3-beam plan with ST. All arc plans used 20 directions and 720 initial layers and 360 final layers.

Results: The results for the phantom targets are shown in Figure 1. Arc+ST plans are more conformal than the Arc+Coll plans, which in turn are more conformal than the 3-Beam plans. The homogeneity is on the same level or better for the Arc+ST plans. When performing a robustness analysis, the worst-case value for CTV D95 is on the same level for all types of plans. The higher conformity of Arc+ST comes at the expense of slightly higher doses to the External volume. Similar trends are seen in the more complex H&N case (see Figure 2), except for the mean dose to External, which is not higher in the Arc+ST plans. Doses to all OARs are reduced using Arc+ST. Improved plan quality can be seen using ST also for 3 beams, but not to the same level as for Arc+ST.